1. Field of the Invention
The present invention relates to a variable dispersion compensator, which compensates for dispersion that develops in an optical signal due to its propagation through an optical transmission line such as an optical fiber transmission line, and an optical transmission system in which it is provided.
2. Description of the Related Art
In an optical transmission system in which optical signals are propagated by optical fiber transmission lines and the like, dispersion accumulates in optical components of each frequency (each wavelength) that is included in an optical signal through the dispersion that exists in an optical fiber, In this regard, it is desired that the amount of dispersion in an optical transmission system be reduced in the frequency band that includes optical signal frequencies in order to suppress waveform deterioration of an optical signal due to propagation along an optical transmission line. In addition, in wavelength division multiplexing (WDM) transmission systems, which propagate multi-wavelength optical signals, in the same manner, it is necessary to reduce the amount of dispersion in the frequency band that includes optical signal frequencies (optical signal wavelengths) of the respective multi-wavelength optical signals.
To compensate dispersion that accumulates in each frequency component of an optical signal, a dispersion compensator is provided upon an optical transmission line. With a dispersion compensator, the dispersion that develops in an optical signal is compensated by applying an appropriate phase shift to an optical signal. Such an optical compensator is disclosed in, for example, Document 1 [The Journal of the Institute of Electronics, Information and Communication Engineers (Shingaku Gihou) Vol. 100, No. 379, OCS2000-61], Document 2 [O plus E Vol. 22, No. 9, p. 1151], and Document 3 [OFC2000, Shirasaki, et al., Variable Dispersion Compensator Using The Virtually Imaged Phased Array (VIPA) for 40-Gbit/s WDM Transmission Systems].